For many years there has been a need to compound batches of liquid materials from liquid constituents where each batch may be of a different composition and volume. In order that the same equipment may be utilised to prepare successive batches elaborate control systems are necessary in order to ensure that constituent liquids are mixed in precisely the correct quantities. To this end a number of systems have utilised fluid flow in order to gauge the correct volume of constituents. Such systems additionally utilise dedicated computerised controllers. Systems with dedicated controllers and utilising the flow of ingredients to ensure accuracy have for example been utilised in the textile industry. The use of fluid flow as a measure of constituents involves the use of complicated valves and other hardware and the use of dedicated controllers is expensive. It is accordingly an object of the present invention to ameliorate one or more of the lastmentioned disadvantages with existing systems or at least to provide the market with an alternative.